DESCRIPTION OF THE BACKGROUND ART
In the production of various cans which comprise a can wall running around the can axis and at least one separation element running at least partly transversely to the can axis, a first contact surface of the can wall is tightly connected by a pressing process to a second contact surface of the separation element, which surface can be laid against the first surface. The separation element is formed, for example, as a base, lid or closure membrane.
In the case of cans, it is known that the base and/or lid or at least parts of the first and/or second contact surfaces can be provided with a sealing material in order to be able to achieve a tight connection by pressing together the contact surfaces and supplying heat. In order to achieve a good compression effect, the press apparatuses used are, for example, those in which the--particularly annular--contact surfaces are introduced between inner and outer conical ring parts while the ring parts are then moved toward one another by an axial movement. Furthermore, the conical press surfaces also result in the formation of a conical connection, which is undesirable in many cans.
It is true that Swiss Patent 659,633 discloses a can whose end face is closed by means of a raised diaphragm. However, a feature essential to that invention is a heat-conducting lid which remains in the can until the latter is opened by the end user (FIG. 9), whereupon the diaphragm too is removed and the can no longer complies with the claim. An intermediate product according to Swiss Patent 659,633 which is suitable for filling at the open opposite end prior to final sealing, has a heat-conducting lid which makes the can expensive and complicated.
With the can disclosed in FIG. 9 of Swiss Patent 659,633, the internal diameter of the heat-conducting lid must in fact exactly correspond to the internal diameter of the can minus twice the diaphragm wall thickness, with the result that wrinkles and creases can be established in the foil edge region during deep drawing.
In a further solution according to the prior art, for example, a cylindrical pipe section having a circular cross-section is separated along square sides with sectional planes parallel to the axis, the corners of the square being inside or outside the wall of the pipe section and the sectional planes each leading in a middle region through the interior of the pipe section. This gives rise to four outer and four inner, essentially triangular press parts, each with a part of the cylindrical press surface. For pressing, the outer press parts and carried by these, also the inner press parts are brought together. Because the sliding surfaces between the outer and the inner press parts are transverse to the contact surfaces to be pressed, the acute-angled ends of the press surfaces of the inner press parts may lead to injuries or creases in the pressed contact surface. In order to keep these defects as small as possible, pressing must be carried out as far as possible exactly with the radius of the pipe section, which is frequently not possible owing to tolerances of the can parts.
EP 007 487 discloses a press apparatus having a table which is vertically displaceable on a support element and having a pressure means with two segments whose outward-pointing edges can be used as press surfaces. Resting on one conical surface of the support element are beveled contact surfaces of two transverse webs, which transverse webs are each connected to a segment and are displaceably mounted on the table perpendicularly to the axis of the support element. In order to press a cylindrical contact region of the can membrane, running around a can axis, against the inner wall regions of a can by means of the press surfaces of the two segments, the table together with the can must be pressed or moved downward. A substantial disadvantage of this solution is that the table with the can must be pressed downward. Even if the compression force is not transmitted by the can to the table, the can must be pressed against the table from the top during the movement of the table, which entails a complicated construction for holding cans of different sizes or, in the case of inadequately held cans, gives rise to problems with the exact insertion of the separation element. A further disadvantage is that the movement toward the contact region, required for pressing, takes place only in the direction of the transverse webs or in the central regions of the segments. Accordingly, the contact region will be slightly deformed to an oval shape during pressing and the compression is weaker in the flattened regions.